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Why did Fisker choose a high revving GM 4 cylinder motor as a generator instead of a diesel motor?

A diesel generator can run at lower rpm's (less noise, better fuel economy/more efficient, longevity etc), plus packaging wise it would be an easier fit than the current 2.0 GM motor. Will they be using BMW Gas engine or diesel engine in the future? Only downside I can think of is the cost...
 

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EV Driver said:
Why did Fisker choose a high revving GM 4 cylinder motor as a generator instead of a diesel motor?

A diesel generator can run at lower rpm's (less noise, better fuel economy/more efficient, longevity etc), plus packaging wise it would be an easier fit than the current 2.0 GM motor. Will they be using BMW Gas engine or diesel engine in the future? Only downside I can think of is the cost...
I think the short version is that diesels are a hard sell for the American market. Fairly or not, I think diesel is viewed as a less clean, less refined and less efficient alternative to gasoline engines in the US. It doesn't help that diesel fuel is on average considerably more expensive here compared to even high octane gasoline.

I would love to see Fisker offer alternatives for the range extender, including diesel, CNG or even hydrogen, but for now I think the only market viable alternative was a gasoline ICE.
 

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LonePalmBJ said:
EV Driver said:
Why did Fisker choose a high revving GM 4 cylinder motor as a generator instead of a diesel motor?

A diesel generator can run at lower rpm's (less noise, better fuel economy/more efficient, longevity etc), plus packaging wise it would be an easier fit than the current 2.0 GM motor. Will they be using BMW Gas engine or diesel engine in the future? Only downside I can think of is the cost...
I think the short version is that diesels are a hard sell for the American market. Fairly or not, I think diesel is viewed as a less clean, less refined and less efficient alternative to gasoline engines in the US. It doesn't help that diesel fuel is on average considerably more expensive here compared to even high octane gasoline.

I would love to see Fisker offer alternatives for the range extender, including diesel, CNG or even hydrogen, but for now I think the only market viable alternative was a gasoline ICE.
Weight may also be a factor since diesel engines typically weigh more than the gas engines of similar output because of the higher compression used by Diesel engines. Another possible factor is that you don't typically see sub 2.0L Diesel engines putting out anything like the horsepower you can extract from small gasoline engines. Also, Gasoline is pretty much universally available in the US, whereas Diesel fuel is not sold at every gas station. Finally, the requirement for Urea injection would add another storage system and added complexity to an already complicated car.

What surprised me more was that Fisker did not go with a Wankel rotary engine, which theoretically anyway, gives you a lot more power for the same displacement.
 

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Discussion Starter · #4 ·
Fabulist said:
LonePalmBJ said:
EV Driver said:
Why did Fisker choose a high revving GM 4 cylinder motor as a generator instead of a diesel motor?

A diesel generator can run at lower rpm's (less noise, better fuel economy/more efficient, longevity etc), plus packaging wise it would be an easier fit than the current 2.0 GM motor. Will they be using BMW Gas engine or diesel engine in the future? Only downside I can think of is the cost...
I think the short version is that diesels are a hard sell for the American market. Fairly or not, I think diesel is viewed as a less clean, less refined and less efficient alternative to gasoline engines in the US. It doesn't help that diesel fuel is on average considerably more expensive here compared to even high octane gasoline.

I would love to see Fisker offer alternatives for the range extender, including diesel, CNG or even hydrogen, but for now I think the only market viable alternative was a gasoline ICE.
Weight may also be a factor since diesel engines typically weigh more than the gas engines of similar output because of the higher compression used by Diesel engines. Another possible factor is that you don't typically see sub 2.0L Diesel engines putting out anything like the horsepower you can extract from small gasoline engines. Also, Gasoline is pretty much universally available in the US, whereas Diesel fuel is not sold at every gas station. Finally, the requirement for Urea injection would add another storage system and added complexity to an already complicated car.

What surprised me more was that Fisker did not go with a Wankel rotary engine, which theoretically anyway, gives you a lot more power for the same displacement.
Most of the HP out of a Wankel motor comes at 7k+ RPM ....Running a Wankel as a generator would mean heavier fuel consumption.

With a diesel motor (such as the 2.0 TDI) the fuel consumption from the generator would go down by at least 25%. In Europe I think this would be a popular option. I am guessing Europe probably represents a significant amount of Karma sales (Surf was chiefly designed for Europe.)

For the amount that you have to actually top up this vehicle (I am guessing the average owner probably fills up 1-2x a month), I don't think finding a diesel station may be that big of a problem?

I would buy one if the engine was diesel (more longevity less problems down the road). Plus I could run it on Bio...

Interestingly enough I believe Fisker used a diesel emissions company for the emissions work on the Karma.
 

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Diesel would be superior in almost all respects except for two: marketing (in the US), and the tendency for the fuel to gel up at low temperatures (especially if you use pure biodiesel; even worse with SVO, straight vegetable oil) which might require electrically heating the fuel tank and lines.

The biggest problem is probably marketing. For the Karma there was also the problem of obtaining something off-the-shelf, which is why only the Nina has the nicer BMW engine.
 

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I have a new range rover evoque and the little inline 4 turbo is a pistol, maybe tata and fisker will work a deal ;) jag dealer networks and range rover engine and customers couldn't hurt either.
 

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ct-fiskerbuzz said:
For the Karma there was also the problem of obtaining something off-the-shelf, which is why only the Nina has the nicer BMW engine.

This is exactly it. At the time around 2008 there was only one 4 cylinder 2.0L or less engine that could do at least 260hp with the balance of weight and NVH they were looking for. BMW didn't have the NINA 4cylinder avilable yet, nor did AUDI have a solution. the motor is still potent, in other applications, there was a facotry kit for 600$ that boosted output to 300hp while maintaning warranty. it also has a pretty solid track record for being low maintance and with few issues. it may have commong from humble origins, but it is a solid little engine.

Diesel (ignoring the current emissions requirements) are going to be heavier and the packaging is going to be bigger. the Ecotec SIDI, isn't that big of an engine, its everything else packed into the engine bay between the frame rails that make it looker bigger than it is.
 

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I know this may sound silly, but is Fisker running the engine in the most efficient manner? I know that it does the start/stop, as I was at zero battery level, and put it in park while talking on the phone, and the engine cut off until I started backing into my garage after the phone call.

What exactly are the RPMs that it runs at and the electrical generation levels associated with it and the fuel consumption as well? I assume there is a chart somewhere with those three curves plotted on it.

Basically, if the engine is running, I would believe that even if the demand is not there for electricity, is the engine idling at an inefficient RPM, when it could be running optimal RPM and producing electricity to charge the battery? I must think that the engineers thought of all this, but there are many times factors other than engineering that play into decisions, i.e. not worrying about efficiency, so that it can be easily improved later by actually working on the efficiency.

I understand that in Sport Mode you want the extra 175kw available at a moments notice, but in Stealth Mode, would it be more efficient to run the engine at full bore and charge the battery as quickly as possible, so that the engine could be shut down, until the battery is depleted again? Is the issue battery degredation, if this was done, and why it is not?

As for Wankels, I would love to see them use a Freedom Motors rotary someday.
 

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kabalah70 said:
I know that it does the start/stop, as I was at zero battery level, and put it in park while talking on the phone, and the engine cut off until I started backing into my garage after the phone call.
I assume you mean Zero miles since the battery is not supposed to go below 15% charge, and even at that level, there is enough power to get the car started and moving along before the ICE has to start up to replenish it. Given how the car behaves at Zero range in Stealth mode, I would assume that the battery is used like a flywheel to initially move the car from a dead stop and to start the engine and then spun back up with the engine replacing the charge used back up to 15%.

kabalah70 said:
I must think that the engineers thought of all this, but there are many times factors other than engineering that play into decisions, i.e. not worrying about efficiency, so that it can be easily improved later by actually working on the efficiency.
If we can use emissions level as a stand in for efficiency, I would think that the engineers tried to get the maximum possible efficiency by reducing the emissions level to the minimum possible level.

kabalah70 said:
As for Wankels, I would love to see them use a Freedom Motors rotary someday.
I read some reports that the Audi A3 Etron was supposed to use a Wankel range extender that ran at 5000RPM. But this was some time ago and I am not sure they are still planning on doing that or if they ended up with a standard reciprocating engine. I would love to see a jet turbine, but that seems equally unlikely, at least for the immediate future.
 

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I think what we all really wanted was what Jaguar did with their EVer Prototype car.....although for production I understand they are going with a conventional ICE as well.

http://www.bladonjets.com/

I want one of these very badly! :p
 

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Fab,

Yes, I meant zero battery range. As for emissions, I don't know how they are measured. I imagine in a manner that is not condusive to the most efficient method for hybrids.
According to this website, it is either mass per distance, or mass per unit of energy produced by the engine.
http://www.dieselnet.com/standards/intro.html
I would imagine the Fisker Karma engine/generator combo has an efficiency curve that looks somewhat like a bell curve, with some sort of distortion or skew, whatever it may be, but the general gist is that it starts out with low efficiency, works to its peak, and then falls back off.
Measuring emissions by the first method: mass/distance, adjusting engine/generator output to minimize emissions would not have the engine operating at its optimal energy output. This would be clearly demonstrated by doing the emissions test using the second method and seeing that when the engine/generator is most efficient, it will produce the least pollution.
Thus, in Stealth Mode, when the engine is turned on, it may be more efficient to run the eng/gen at the most efficient RPM regardless of demand and place the extra energy into the battery. This would also result in the least emissions per energy produced which is the most logical way to doing things.
 

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kabalah70 said:
Fab,

Yes, I meant zero battery range. As for emissions, I don't know how they are measured. I imagine in a manner that is not condusive to the most efficient method for hybrids.
According to this website, it is either mass per distance, or mass per unit of energy produced by the engine.
http://www.dieselnet.com/standards/intro.html
I would imagine the Fisker Karma engine/generator combo has an efficiency curve that looks somewhat like a bell curve, with some sort of distortion or skew, whatever it may be, but the general gist is that it starts out with low efficiency, works to its peak, and then falls back off.
Measuring emissions by the first method: mass/distance, adjusting engine/generator output to minimize emissions would not have the engine operating at its optimal energy output. This would be clearly demonstrated by doing the emissions test using the second method and seeing that when the engine/generator is most efficient, it will produce the least pollution.
Thus, in Stealth Mode, when the engine is turned on, it may be more efficient to run the eng/gen at the most efficient RPM regardless of demand and place the extra energy into the battery. This would also result in the least emissions per energy produced which is the most logical way to doing things.
I was told by one of the service people that the engine runs mostly at 2 speeds - idle and 2400 (I believe) RPM. The road show cars could run all the way to the redline, but they found that at 2400 RPM they were generating 97% of the current they could produce at 6000 PRM, and lots of journos/drivers complained about the engine noise.

Again, this was from a service person, not a Fisker engineer, but he seemed to know what he was talking about.
 

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Fab....I've noticed several times you referenced that the car should not drop below 15% charge. With mine it will routinely run all the way down to 0% charge and I have pushed 4-5 miles out of it showing 0%...if I am in stealth mode I need to manually shift to sport mode to get the ICE to kick in. On a recent long road trip running in sport the generator powered me back up to the 26 mile mark.
Does your engine automatically kick in when you reach that 15% level?
These sure are curious vehicles!
 

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kabalah70 said:
Fab,

I would imagine the Fisker Karma engine/generator combo has an efficiency curve that looks somewhat like a bell curve, with some sort of distortion or skew, whatever it may be, but the general gist is that it starts out with low efficiency, works to its peak, and then falls back off.
Here is the torque/horsepower curve for the Ecotec LNF enginet that I found on one of the GM hobbyist forums:



The torque curve on this engine is extremely flat. Not sure if that has correlation to fuel consumption or is it the HP curve that correlates to that.
 

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Grebechini said:
Fab....I've noticed several times you referenced that the car should not drop below 15% charge. With mine it will routinely run all the way down to 0% charge and I have pushed 4-5 miles out of it showing 0%... [snip]
He's talking about the actual battery charge; you're looking at the number displayed on the dashboard. "0%" on the dashboard means "15% in the battery".

The Karma does not go to the extremes of the Volt (because it has a better battery technology) but the Volt illustrates the issue pretty well: for battery life purposes, the Volt only charges the battery to about 85%, and only drains it to about 20%, hence using about 65% of the battery's actual kWh-storage-range. When the battery is at 85% the car says "I'm full" and stops charging, and when it's at 20% the car says "out of battery" and requires the gasoline engine to run. If the dashboard gauge reads "half full", you're halfway between 20 and 85 percent. This article goes into more detail.

The advantage to using only some of the battery's overall charge-range is that it lasts longer. The disadvantage is that you're hauling around a lot of weight that you're "not using", as it were. Because A123's chemistry is better, they can use more than 80% of the total kWh-storage, vs the 65% in the Volt.
 

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ct-fiskerbuzz said:
He's talking about the actual battery charge; you're looking at the number displayed on the dashboard. "0%" on the dashboard means "15% in the battery".
That's actually 0 miles on the center display of battery miles left, not %. If you look at the battery "fuel" gauge on the right when 0 miles are shown, it is at approximately 15% of the real estate it can light up.

My car typically kicks in the ICE within less than a mile of reaching 0 on the center battery miles guage.
 

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Ct & Dennis...
Thanks for clearing that up...I'll keep an eye on the battery "Fuel" gauge next time...and here I thought those two were redundant.
 

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Grebechini said:
Fab.....if I am in stealth mode I need to manually shift to sport mode to get the ICE to kick in.
@Grebechini: If your car is working correctly, there is no need to switch to Sport mode when the miles get down to zero. The generator should come on automatically and keep the car going without you having to do anything when the battery gets down to 15%. The display stays in Stealth or Hill mode when this happens and the only indication is the sound of the engine and the Temperature Warning light that flashes very briefly. If your car is not doing this, you should have the dealer check it.
 

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Fab,
If what you say is true about the engine running at idle and 2400 RPM, I would like to know the generator output at idle is as you say you think at 2400 RPM it is 97% of its max of 175 kw. Fuel consumption at those RPMs would be nice to so that fuel consumption per KW could be compared.
In other news, but slightly related, I noticed my car running the engine in Stealth Mode today with the batt fully charged almost right out of the garage. I assume the battery was too cold. It would be nice if the driver got some kind of indication as to why the engine is on when it is on: Fuel cycling, coolant warming, battery depleted, engine exercise for lube/emissions, etc.
 

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kabalah70 said:
Fab,
If what you say is true about the engine running at idle and 2400 RPM, I would like to know the generator output at idle is as you say you think at 2400 RPM it is 97% of its max of 175 kw. Fuel consumption at those RPMs would be nice to so that fuel consumption per KW could be compared.
In other news, but slightly related, I noticed my car running the engine in Stealth Mode today with the batt fully charged almost right out of the garage. I assume the battery was too cold. It would be nice if the driver got some kind of indication as to why the engine is on when it is on: Fuel cycling, coolant warming, battery depleted, engine exercise for lube/emissions, etc.
You are a curious dude aren't you? Maybe it's female and just feels left out cause you're not calling on it enough?
 
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